Method and device for controlling an internal combustion engine

ABSTRACT

The invention relates to a method and device for controlling an internal combustion engine comprising an inlet pipe leading to a cylinder input where a gas input valve is placed. Said engine also comprises a drive for the gas input valve which makes it possible to adjust a gas input valve lift for at least two values. The engine also comprises an injection valve for metering fuel and a spark plug which controls the crankshaft angle of air-fuel mixture ignition. Said internal combustion engine is controlled in a following manner: a fuel is metered at least once during the intake stroke of a cylinder when the valve lift (VL) passes from one value to the other and at least one final injection is carried out in a dosing manner only when the valve lift (VL) is really carried out.

CROSS REFERENCE TO RELATED APPLICATION

This application is the US National Stage of International ApplicationNo. PCT/EP2004/052906, filed Nov. 10, 2004 and claims the benefitthereof. The International Application claims the benefits of GermanPatent applications No. 10356257.5 DE filed Dec. 2, 2003, all of theapplications are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention relates to a method and device for controlling an internalcombustion engine

BACKGROUND OF THE INVENTION

Increasingly high demands are made on internal combustion engines withregard to their performance and efficiency. At the same time, because ofstringent legal regulations, the emissions must also be low. Suchrequirements can be met properly if the internal combustion engine isequipped with gas-changing valves and corresponding drives for thisinternal combustion engine in which the valve lift curve differsdepending on the operating point of the internal combustion engine.Because of this, throttle losses in the case of air intake can bereduced and, if required, higher exhaust gas recirculation rates canquickly be set.

Adjusting the valve lift of a gas intake valve of the internalcombustion engine between a lower and a higher valve lift is known. ThePorsche 911 Turbo for example is thus equipped with a device foradjusting the valve lift of the gas intake valve and the gas outletvalve. In addition, the internal combustion engine of this vehicle isprovided with a camshaft on which for each gas intake valve, one camwith a lower lift and two additional cams with a higher lift areembodied. The cam lift is transferred by means of a transfer unit to thegas intake valve. The transfer unit is embodied as a cup-shaped tappetcomprising a cylinder element and a ring cylinder element arrangedconcentrically to this cylinder element. The cam with a lower lift actson the cylinder element while the cams with the higher lift act on thering cylinder element. Depending on a switch position of the cup-shapedtappet, either the lower or the higher lift is transferred to the gasintake valve. While the internal combustion engine is idling, the lowercam lift is transferred to the gas intake valve. This results in lowerfrictional losses based on the small diameter of the cam and thecylinder element used in this mode of operation and the lower valvelift.

In addition, a higher loading movement is achieved. This enables theemissions of the internal combustion engine to be decreased and at thesame time, the fuel consumption to be kept low. The lower valve lift ismaintained in the case of a lower and average load. Throttle losses canalso be reduced by a corresponding phase adjustment between the gasintake valve and the gas outlet valve and a resulting internal exhaustgas recirculation rate. In the case of higher load requirements made onthe internal combustion engine, the valve lift passes to the highervalue. For a high driving comfort of a vehicle in which such an internalcombustion engine is arranged and for low emissions of noxioussubstances, it is important that the passage from the lower valve liftto the higher valve lift takes place without misfiring.

SUMMARY OF THE INVENTION

The object of the invention is to create a method and a device forcontrolling an internal combustion engine which ensures that lowemissions of noxious substances are generated.

The object of the invention is solved by the features of the independentpatent claims. Advantageous embodiments of the invention arecharacterized in the subclaims.

The invention is characterized by a method and a corresponding devicefor controlling an internal combustion engine comprising an intake pipeleading to a cylinder intake where a gas intake valve is placed. Saidengine also comprises a drive for the gas-changing valve, which makes itpossible to set a gas intake valve lift for at least two values. Theengine also comprises an injection valve for metering the fuel and aspark plug which controls the crankshaft angle of the air/fuel mixtureignition. Said internal combustion engine is controlled in the followingmanner: fuel is metered at least once during the intake stroke of acylinder, when the valve lift passes from one value to the other and atleast one final injection is carried out in a dosing manner only whenthe valve lift has actually been carried out. Therefore, it can easilybe ensured in this manner that no misfiring or combustion with very highfuel excess takes place, therefore, a considerably larger amount of fuelthan the stoichiometric air/fuel ratio occurs even if it is verydifficult to predict when an actual valve lift will pass from one valueto the other value.

In an advantageous embodiment of the method for controlling the internalcombustion engine, fuel is metered at least once during the intakestroke of a cylinder and the amount of fuel is determined depending onwhether or not the passage of the valve lift from one value to the othervalue has actually been carried out. This has the advantage that it isvery easy to implement.

In an additional advantageous embodiment of the method for controllingan internal combustion engine, fuel is metered at least once during theintake stroke of a cylinder without taking into consideration whether ornot the passage of the valve lift from one value to the other value hasactually been carried out. Because of this a proper preparation of theair/fuel mixture can be guaranteed, the requirement being a propercombustion process and accordingly low emissions of noxious substancesof the internal combustion engine.

In an additional advantageous embodiment of the method, at least onefinal injection is carried out in a dosing manner only when the valvelift passage from one value to the other value has actually been carriedout. Because of this, a very advantageous mixture preparation can simplybe guaranteed, on the one hand, if the value with a lower valve lift wasactually set and, therefore, low emissions of noxious substances wereensured. On the other hand, a desired air/fuel ratio can also be set ifthe value with a higher valve lift has actually been set.

In an additional advantageous embodiment of the method, the amount offuel which is metered without taking into consideration whether or notthe passage of the valve lift from one value to the other value hasactually been carried out, is determined in such a way that there is adesired air/fuel ratio when the valve lift has actually been carried outwith the value with a lower valve lift. Because of this, the mixture cansimply be prepared very thoroughly and an air/fuel ratio can be setexactly if the value has actually been set with a lower lift.

In an additional advantageous embodiment of the method, the amount offuel which is metered without taking into consideration whether or notthe passage of the valve lift from one value to the other value hasactually been carried out, is determined in such a way that the amountof fuel is higher than the desired air/fuel ratio if the valve lift hasactually been carried out with the value with a lower valve lift. Thishas the advantage of an improved mixture preparation if the value with ahigher valve lift has actually been set.

In an additional advantageous embodiment of the method, fuel is meteredat least once during the intake stroke of a cylinder, when the valvelift passes from one value to the other and at least one final injectionis carried out in a dosing manner only when the valve lift has actuallybeen carried out if the rotational speed is greater than a predeterminedthreshold value which preferably is approximately 2000 revolutions perminute. This has the advantage that, on the one hand, the cost ofdetermining the amount of fuel to be metered is reduced to below thisthreshold value and, on the other hand, surprisingly enough, theprobability that the valve lift will not pass to another value isconsiderably higher for rotational speeds exceeding the predeterminedthreshold value than for rotational speeds below the predeterminedthreshold value and therefore the risk of misfiring is small.

In an additional advantageous embodiment of the method, the ignitionangle is adapted depending on a variable which characterizes themetering of fuel and which depends on whether or not the valve liftpassage from one value to the other value has actually been carried out.This has the advantage that a possibly poorer mixture preparation can betaken into consideration when setting the ignition angle and indeed insuch a way that lower emissions of noxious substances are guaranteed.

An additional advantageous embodiment of the method is the variable ofthe amount of fuel and/or the crankshaft angle of metering the fuel,which depends on whether or not the valve lift passage from one value tothe other value has actually been carried out. This has the advantagethat these variables are characteristic of the mixture preparation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in detail below as an embodiment on the basisof the accompanying drawings. They are as follows:

FIG. 1 an internal combustion engine with a control unit,

FIG. 2 an additional view of parts of the internal combustion engine inaccordance with FIG. 1,

FIG. 3 a flowchart of a first embodiment of a program for controlling aninternal combustion engine for a desired passage of the valve lift froma lower valve lift to a higher valve lift,

FIG. 4 a flowchart of the program in accordance with FIG. 3 forcontrolling an internal combustion engine for a desired passage of thevalve lift from a higher valve lift to a lower valve lift and

FIGS. 5 and 6 an additional embodiment of a program for controlling aninternal combustion engine.

DETAILED DESCRIPTION OF THE INVENTION

Elements with the same design and function are characterized in all thefigures with the same reference symbols.

An internal combustion engine (FIG. 1) includes an intake tract 1, anengine block 2, a cylinder head 3 and an exhaust gas tract 4. The intaketract preferably includes a throttle valve 11, a manifold 12 and anintake pipe 13, which is guided to a cylinder Z1 via an intake port inthe engine block. The engine block also includes a crankshaft 21, whichis connected to the piston 24 of a cylinder Z1 by means of a connectingrod 25.

The cylinder head includes a drive with an intake valve 30, an exhaustvalve 31 and valve gears 32, 33. The gas intake valve 30 and the gasexhaust valve 31 are driven by means of a camshaft 36 (see FIG. 2) onwhich cams 39, 39 a and 39 b are embodied for driving the gas intakevalve 30. In addition, cams which are not shown are provided on anadditional camshaft which drive the gas intake valve 31.

A total of three cams 39, 39 a, 39 b (FIG. 2) are allocated to the gasintake valve 30. The cams 39, 39 a, 39 b drive the gas-changing valve 30via a transfer unit 38. The transfer unit 38 is embodied as a cup-shapedtappet. It includes a cylinder element 38 a and a ring cylinder element38 b arranged concentrically to the cylinder element. A cam 39 drivesthe cylinder element 38 a. The cams 39 a, 39 b drive the ring cylinderelement 38 b. In a switching position of the cup-shaped tappet, only thelift of the cam 39, which is lower than the cam 39 a and b, istransferred to the gas intake valve 30. In an additional switchingposition of the cup-shaped tappet, the lifts of the cams 39 a and b aretransferred to the gas intake valve 30. The switching position of thecup-shaped tappet can be achieved by a corresponding activation of anactuator provided in the cup-shaped tappet and preferably takes placehydraulically.

However, the drive 31, 32 can also be embodied in an alternative way.The camshaft can for example be embodied in such a way and engage withan actuator so that, depending on the desired valve lift, different camsdrive the gas changing-valve.

The cylinder head 3 (FIG. 1) also includes both an injection valve 34and a spark plug 35. Alternatively, the injection valve can also bearranged in the intake pipe 13.

The exhaust gas tract 4 includes a catalytic converter 40. From theexhaust gas tract 4, an exhaust recirculation line can be guided to theintake tract 1, particularly to the manifold 12.

In addition, a control unit 6 is provided to which sensors have beenallocated, said sensors detecting the different measured quantities andin each case determining the measured value of the measured quantity.The control unit 6 determines, in accordance with at least one of themeasured quantities, the controlling variables which are then convertedinto one or several adjusting signals for controlling the final controlelements by means of corresponding actuators.

The sensors are a pedal position indicator 71 which detects the positionof an acceleration pedal 7, an air mass flow meter 14 which detects anair mass flow upstream of the throttle valve 11, a temperature sensor 15which detects the intake air temperature, a pressure sensor 16 whichdetects the intake pipe pressure, a crankshaft angle sensor 22 whichdetects a crankshaft angle to which a rotational speed N is allocated, afurther temperature sensor 23 which detects a coolant temperature, acamshaft angle sensor 36 which detects the camshaft angle, a furthertemperature sensor which detects an oil temperature and an oxygen sensor41 which detects a residual oxygen content of the exhaust gas and, ifrequired, a sensor which detects whether or not the gas intake valve 30is operated with a lower or a higher valve lift. Depending on theembodiment of the invention, there can be any subset of the mentionedsensors or even additional sensors.

The final control elements are, for example, the throttle valve 11, thegas intake and the gas exhaust valves 30, 31, the injection valve 34,the spark plug 35, the setting mechanism 37 or the transfer unit 38.

In addition to the cylinder Z1, the internal combustion engine can alsohave other cylinders, namely the cylinders Z2, Z3, Z4 to whichcorresponding sensors and final control elements are allocated andcontrolled accordingly. The control unit 6 conforms to a device forcontrolling the internal combustion engine.

A program for controlling the internal combustion engine is preferablystarted when the internal combustion engine is started. The start takesplace in a first step S1 (FIG. 3), in which variables are initialized,if required.

In a step S2, a test is performed to determine whether or not thecurrent rotational speed N is greater than a predetermined thresholdvalue N_THR of the rotational speed, which preferably is approximately2000 revolutions per minute. If the condition of step S2 has not beenmet, a third amount of fuel MFF3 is determined in a step S6 with dueconsideration of the air mass in the cylinder to be expected for thisoperating cycle, in which case for this purpose the desired step of thevalve lift VL is used as a basis and with due consideration of theair/fuel ratio to be set. In addition, the metering of the third amountof fuel MFF3 is then controlled in a step S6.

On the other hand, if the condition of a step S2 has been met, a test isthen performed in a step S4 to determine whether or not since the lastoperating cycle of the cylinder Z1, a passage of the valve lift VL froma lower valve lift LO to a higher valve lift HI was requested.

If this is not the case, processing will continue in a step S6.Subsequently to a step S6, the processing will be continued in a step S8in which an ignition angle IGN is then determined depending on therotational speed N, a desired torque TQ_REQ and, if required, additionalvariables. In this way, for example, instead of the desired torqueTQ_REQ, another variable representing the load of the internalcombustion engine can also be used. In addition, the ignition angle IGNcan also be determined depending on additional variables with regard tothe desired minimizing of emissions of noxious substances such as NOXemissions.

The program then remains in a step S10 for a predetermined waitingperiod T_W or also for a predetermined crankshaft angle beforeprocessing is continued anew in a step S2.

On the other hand, if the condition of a step S4 is met, a first amountof fuel MFF1 is determined in a step S12 and the first amount of fuelMFF1 is for example determined in such a way that a desired air/fuelratio has been set in the cylinder Z1, on the condition that the valvelift VL of the gas intake valve 30 is lower than in the current intakestroke of the lower valve lift LO. In addition, the actual metering ofthe first amount of fuel MFF1 is then controlled in a step S12.Alternatively, in a step S12, the first amount of fuel MFF1 can thenalso be selected in such a way that there is a higher amount of fuel inthe cylinder Z1 than the desired air/fuel ratio, on the condition thatthe valve lift VL of the gas intake valve 30 is the lower valve lift LO.

The program then remains in a step S14 for a predetermined waitingperiod T_W, which can differ from that of step S10. The waiting periodT_W in a step S14 preferably has to be metered in such a way that in thecase of a subsequent processing of a step S16 it is possible todetermine whether or not the valve lift VL in the current intake lift isactually the lower valve lift LO or actually the higher valve lift HI.However, it is metered so low that a step S16 can possibly be finishedearly.

The actual valve lift VL is preferably either determined by means of thesuitable sensor or in a simple embodiment the passage from a lower valvelift LO to a higher valve lift HI can take place on the basis of thecurve of the intake pipe pressure or also on the basis of the curve of ahydraulic pressure, in the case in which the passage takes placehydraulically or is also detected on the basis of electrical signals ifthe passage takes place electrically. In this way, it is for examplepossible to determine on the basis of the actual curve of the intakepipe pressure, while the gas intake valve 30 is in its open position, bycomparing with corresponding values for the lower valve lift LO and/orthe higher valve lift HI, whether or not the actual lower valve lift LOor the higher valve lift HI has been set.

If it is detected in a step S16 that the actual valve lift VL is thelower valve lift LO, processing will be continued in a step S8.

On the other hand, if it is detected in a step S16 that the actual valvelift VL is the higher valve lift HI, a second amount of fuel MFF2 isthen determined in a step S18. The second amount of fuel MFF2 is thendetermined in such a way that the sum of the first and the second amountof fuel MFF1, MFF2 corresponds with the desired air/fuel ratio in thecylinder Z1 in the case of the higher valve lift HI. In addition, themetering of the second amount of fuel MFF2 is controlled in a step S18.

A correction value IGN_COR is then determined in a step S20 for theignition angle IGN and indeed depending on the second amount of fueland/or the crankshaft angle CRK_MFF2 of the metering of the secondamount of fuel MFF2. Because of this correction value, the quality ofthe mixture preparation, which has possibly decreased because of themetering of the second amount of fuel MFF2 occurring only at a laterstage, can be determined and in this way by influencing the ignitionangle IGN the minimizing of emissions of noxious substances can beensured.

The ignition angle IGN is then determined in a step S22 depending on thecorrection value IGN_COR, the rotational speed, the desired torqueTQ_REQ and, if required, additional or alternative variables, which thespecialist then uses for this purpose. In addition, in a step S22, theignition of the air/fuel mixture in the cylinder Z1 is controlled. Theprocessing is then continued in a step S10. The waiting period T_W in astep S10 should preferably be metered in such a way that subsequent to astep 50, the processing is then continued in a step S2 if a newoperating cycle of the cylinder Z1 has started.

If in a step S12, the first amount of fuel MFF1 is determined in such away that the desired air/fuel ratio has been set for the lower valvelift, it is ensured that the emissions of noxious substances in the caseof an actual non-executed passage of the valve lift from the lower valvelift LO to the higher valve lift HI is minimized. On the other hand, ifin the case of a step S12, a first amount of fuel MFF1 increased forthis purpose has been determined, this indeed still causes increasedemissions of noxious substances in the case where a passage from thelower valve lift LO to the higher valve lift HI did not actually takeplace. This has the advantage that in the case of a possibly moreprobable actual passage from a lower valve lift LO to a higher valvelift HI, an improved mixture preparation based on the earlier meteringof a higher first amount of fuel MFF1 is guaranteed.

Tests have shown that the reason for a deviation between the desired andthe actually set valve lift VL, for example, in the case of a hydraulicsystem can be a foaming-up of the hydraulic fluid while operating theinternal combustion engine. Gas bubbles in this foamed-up fluid lead toa changed compressibility of the fluid which, on the other hand, canlead to the fact that a desired passage did not place in good time.Surprisingly, however, this foaming-up occurred strongly, in particular,above the threshold value N_THR.

The embodiment of the program for controlling an internal combustionengine in accordance with FIG. 4 differs from that in accordance withFIG. 3 in that in a step S4′ a test is performed to determine whether ornot a passage of the valve lift VL from the higher valve lift HI to thelower valve lift LO was requested. In addition, a test is carried out ina step S16′ to determine whether or not the actual valve lift VL passedfrom a higher valve lift HI to a lower valve lift LO. The programs inaccordance with the FIGS. 3 and 4 are preferably finished parallel toeach other.

FIGS. 5 and 6 show an alternative embodiment of the program inaccordance with FIG. 3, in which case likewise only the steps whichdiffer from those in accordance with FIG. 3 are described. A step S4 isfollowed by a step S26 in which the program for the waiting period T_Wremains when change of the valve lift VL from the lower valve lift LO tothe higher valve HI is requested. The waiting period T_W is selected ina step S26 in such a way that a subsequent step S28 is finished if itcan be determined whether or not the valve lift VL actually passed fromthe lower valve lift LO to the higher valve lift. On the other hand, thewaiting period T_W of step S26 is selected in such a way that a step S28is finished as early as possible.

In a step S28 a test is then performed to determine whether or not theactual valve lift VL has changed from the lower valve lift LO up to thehigher valve lift HI.

If this is the case, then in a step S30 the sum of the first and secondamount of fuel MFF1, MFF2 is determined and a metering of the sum of thefirst and second amount of fuel MFF1, MFF2 is controlled. In this way,the metering of both the first and the second amount of fuel MFF1, MFF2,in this case, only takes place in a period of time, in which it alreadyhas been specified whether or not the actual valve lift VL has changedfrom the lower valve lift LO to the higher valve lift HI. In this case,the amount of fuel required for the desired air/fuel ratio can always bemetered reliably in this manner.

The correction value IGN_COR is then determined in a step S32 dependingon the sum of the first and the second amount of fuel MFF1, MFF2 and/orthe crankshaft angle CRK_MFF12 of the metering of the amount of fuel inthe cylinder Z1. The ignition angle IGN is then determined in a step S34depending on the correction value IGN_COR, the rotational speed N, thedesired torque TQ_REQ and, if required, additional variables oralternatively from other variables.

On the other hand, if the condition of a step S28 has not been met, i.e.the actual valve lift VL from the lower valve lift LO to the highervalve lift HI has not changed, the first amount of fuel MFF1 isdetermined in a step S38.

The correction value IGN_COR of the ignition angle IGN is thendetermined in a step S40 depending on the first amount of fuel MFF1and/or the crankshaft angle CRK_MFF1 of the metering of the first amountof fuel MFF1 in the cylinder Z1.

The ignition angle IGN is then determined in a step S42 depending on thecorrection value IGN_COR, the rotational speed N, the desired torqueTQ_REQ and additional variables or alternative variables and theignition is then controlled in the case of the predetermined ignitionangle IGN.

On the other hand, in all the embodiments the metering of the first, thesecond and the third amount of fuel MFF1, MFF2, MFF3 can again bedivided into more than one actual injection. Corresponding programs arealso finished for the additional cylinders Z2-Z4.

1-11. (canceled)
 12. A method for controlling an internal combustionengine, comprising: metering a fuel at least once during an intakestroke of a cylinder when a valve lift passes from one value to anothervalue; and carrying out one final injection in a dosing manner only whenthe valve lift has actually been carried out.
 13. The method inaccordance with claim 12, wherein fuel is metered at least once duringthe intake stroke of a cylinder without taking into considerationwhether or not the passage of the valve lift from one value to the othervalue has actually been carried out.
 14. The method in accordance withclaim 12, wherein at least one final injection is carried out in adosing manner only when the valve lift passage from one value to theother value has actually been carried out.
 15. The method in accordancewith claim 12, wherein the amount of fuel which is metered withouttaking into consideration whether or not the passage of the valve liftfrom one value to another value has actually been carried out isdetermined in such a way that there is a desired air/fuel ratio when thevalve lift has actually been carried out with the value with a lowervalve lift.
 16. The method in accordance with claim 12, wherein theamount of fuel that is metered without taking into consideration whetheror not the passage of the valve lift from one value to the other valuehas actually been carried out is determined in such a way that theamount of fuel is higher than the desired air/fuel ratio if the valvelift has actually been carried out with the value with a lower valvelift.
 17. The method in accordance with claim 12, wherein fuel ismetered once during the intake stroke of a cylinder, when the valve liftpasses from one value to the other and at least one final injection iscarried out in a dosing manner only when the valve lift has actuallybeen carried out.
 18. The method in accordance with claim 12, wherein infuel is metered at least once during the intake stroke of a cylinder,when the valve lift passes from one value to the other and at least onefinal injection is carried out in a dosing manner only when the valvelift has actually been carried out if the rotational speed is greaterthan a predetermined threshold value.
 19. The method in accordance withclaim 18, wherein the threshold value is approximately 2000 revolutionsper minute.
 20. The method in accordance with claim 12, wherein anignition angle is adapted depending on a variable which characterizesthe metering of fuel and which depends on whether or not the valve liftpassage from one value to the other value has actually been carried out.21. The method in accordance with claim 20, wherein the variable is theamount of fuel and/or the crankshaft angle of the metering of the fuel,which depends on whether or not the valve lift passage from one value tothe other value has actually been carried out.
 22. A device forcontrolling an internal combustion engine, comprising: a drive for a gasintake valve by a valve lift of the gas intake valve that can be set forat least two values; an injection valve which meters a fuel; and a sparkplug which controls a crankshaft angle of the air/fuel mixture ignition,wherein the device ensures that fuel is metered at least once during theintake stroke of a cylinder when the valve lift passes from one value toanother and that at least one final injection is carried out in a dosingmanner only when the valve lift has actually been carried out.